Measurement method of distinguishing dew and frost point using quartz crystal microbalance dew-point sensor in low temperature

ABSTRACT

The present invention relates to a measurement method of dew-point in low temperature, and more specifically to a measurement method of accurately distinguishing dew-point and frost-point using a quartz crystal microbalance dew-point sensor in a low temperature of 0° C. or less. To this end, the present invention provides a measurement method of distinguishing dew and frost point using a quartz crystal microbalance dew-point sensor in low temperature, comprising the steps of: measuring a resonant frequency of a quartz crystal microbalance dew-point sensor while slowly dropping temperature; observing shock waves of the resonant frequency; and determining dew point or frost point through the observation of the resonant frequency and shock waves of the quartz crystal microbalance dew-point sensor.

TECHNICAL FIELD

The present invention relates to a measurement method of dew-point inlow temperature, and more specifically to a measurement method ofaccurately distinguishing dew-point and frost-point using a quartzcrystal microbalance dew-point sensor in a low temperature of 0° C. orless.

BACKGROUND ART

A humidity measurement is very important in many fields such asenvironment, food, agriculture, medical care, automobile, textile,semiconductor technology, bio technology, and the like. To this end,various humidity measurement technologies using impedance, capacitance,optical method, surface acoustic wave, etc. have been developed. In thehumidity measurement, the dew-point measurement has been generally usedas a standard method and the dew-point sensor in a chilled mirror typehas been currently used as a standard calibrator in many laboratories.

In fields such as semiconductor, display, ultrapure gas manufacture,etc., a plurality of processes has been performed in very low pressureor vacuum environment. In the case of a semiconductor process, althoughthere is an extremely small amount of moisture in a portion of remainedgas during the process, the moisture has a large effect on physicalproperties of a metal and a semiconductor thin film. Further, since anextremely small amount of moisture causes the same defects even in thecase of the display process, a need exists for a technology capable ofmeasuring an extremely small amount of moisture such as ppm and ppbwithin a minimum space.

Therefore, a need for a technology capable of accurately measuring andanalyzing the dew point in a low humidity environment has beenincreased. A currently commercialized dew-point measurement apparatuscan measure the dew point up to −90° C., but is difficult to accuratelymeasure supercooled dew point due to low accuracy in low temperature.

As one example, in the case of the dew-point measurement apparatus inthe currently generally used chilled mirror type, since it measures aformation of the dew point by means of the optical method, themeasurement apparatus can perform the dew-point measurement only thecase where a dew of 3 μg/cm² or more is produced. Also, when measuringthe dew point in a low temperature between 0° C. and −40° C., liquid dewmay be produced, but solid frost may be produced. However, it is noteasy to distinguish them. The temperature of the dew point (or frostpoint) measured according to whether water drop produced in 0° C. orless is the liquid dew or the solid frost has a large error (about 4°C.) so that the accurate measurement may not be performed. Many methodsto remove such an error have been studied; however, many solutions havebeen currently required.

DISCLOSURE Technical Problem

An object of the present invention provides a new method of recognizinga supercooled dew point using a quartz crystal microbalance dew-pointsensor and provides a dew-point measurement method of accuratelydistinguishing supercooled dew point and frost point in a lowtemperature of 0° C. or less.

Also, another object of the present invention provides a dew-pointmeasurement method of accurately distinguishing dew point, supercooleddew point and frost point by scanning once resonant frequency using aquartz crystal microbalance dew-point sensor in a low temperature,without adding a new system.

Technical Solution

In order to accomplish the aforementioned technical problem, themeasurement method of distinguishing dew and frost point using a quartzcrystal microbalance dew-point sensor in low temperature comprises thesteps of: measuring a resonant frequency of a quartz crystalmicrobalance dew-point sensor while slowly dropping temperature;observing shock waves of the resonant frequency; and determining dewpoint or frost point through the observation of the resonant frequencyand shock waves of the quartz crystal microbalance dew-point sensor.

When observing the resonant frequency of a quartz resonator in thequartz crystal microbalance dew-point sensor while dropping temperature,it is judged that the temperature is the dew point if a transitionphenomenon of the shock wave and the resonant frequency is observed in aresonant frequency pattern of the quartz resonator and the temperatureis the frost point if the transition phenomenon of the shock wave andthe resonant frequency is not observed,

The quartz crystal microbalance dew-point sensor may be configured of aquartz resonator, a Peltier cooler device, a quartz resonator holder,and a platinum resistance temperature sensor.

Slowly dropping the temperature is performed by controlling thetemperature of the quartz resonator using the Peltier cooler device andthe temperature dropped by means of the Peltier cooler device istransferred to the quartz resonator through the quartz resonator holderso that the temperature of the quartz resonator can be controlled.

The quartz resonator holder is made of copper and one surface of thequartz resonator holder may be attached with the platinum resistancetemperature sensor to measure the temperature of the quartz resonatorholder.

The resonant frequency of the quartz resonator is transferred to acomputer via a coaxial cable and may be stored as a function oftemperature by means of the computer.

Advantageous Effects

The measurement method of dew point in low temperature according to thepresent invention has an advantage capable of accurately distinguishingand measuring three waterdrop forms, that is, frost, supercooled dew,and dew, using a quartz crystal microbalance dew-point sensor.

Furthermore, it has an effect that the measurement method can confirmsupercooled dew point in low temperature due to a characteristicfrequency phenomenon of the quartz resonator and can accurately measuresupercooled dew point and frost point by scanning once resonantfrequency without having a further apparatus

DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description ofpreferred embodiments given in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view of a quartz crystal microbalancedew-point sensor;

FIG. 2 is a graph showing resonant frequency characteristics accordingto saturated humid air with respect to an ice of −50° C. to surfacetemperature of a quartz resonator in accordance with a first embodimentof the present invention;

FIG. 3 is a graph showing resonant frequency characteristics accordingto saturated humid air saturated with respect to an ice of −10° C. tosurface temperature of a quartz resonator in accordance with a secondembodiment of the present invention; and

FIG. 4 is a graph showing resonant frequency characteristics accordingto saturated humid air with respect to water of 6.3° C. to surfacetemperature of a quartz resonator in accordance with a third embodimentof the present invention.

BEST MODE

Hereinafter, the embodiments of the present invention will be describedin detail with reference to accompanying drawings. The followingdescribed embodiments are provided, by way of example, so as to fullytransfer the idea of the present invention to those skilled in the art.Therefore, the present invention is not limited to the embodimentsdescribed below and can be embodied in other forms. And, in thedrawings, a length, a thickness, and the like of a layer and a regioncan be emphasized for convenience of explanation. Like referencenumerals refer to like components throughout the specification.

FIG. 1 is a cross-sectional view of a quartz crystal microbalancedew-point sensor according to the present invention. The measurementtechnology of distinguishing dew and frost point using the quartzcrystal microbalance dew-point sensor in low temperature will bedescribed below with reference to the cross-sectional view of the quartzcrystal microbalance dew-point sensor.

Referring to the drawings, the resonant frequency of the quartz crystalmicrobalance dew-point sensor is measured while slowly droppingtemperature of quartz resonator in the quartz crystal microbalancedew-point sensor. The quartz crystal microbalance dew-point sensor maybe configured of a quartz resonator 10, a Peltier cooler device 20, aquartz resonator holder 30, and a platinum resistance temperature sensor40.

Slowly dropping the temperature of the quartz crystal microbalancedew-point sensor may be performed by controlling the temperature of thequartz resonator 10 using the Peltier cooler device 20. Concretelydescribing, the Peltier cooler device 20 is positioned to be contactedto a bottom surface of the quartz resonator holder 30 and the quartzresonator holder is positioned to be contacted to an edge of the quartzresonator 10. Accordingly, the temperature dropped due to the Peltiercooler device 20 is transferred to the quartz resonator 10 through thequartz resonator holder 30 so that the temperature of the quartzresonator 10 can be controlled.

In order to transfer effective temperature from the Peltier coolerdevice 20, the quartz resonator holder 30 may be preferably made ofmaterials with high thermal conductivity, for example, copper.

One surface of the quartz resonator holder 30 may be attached with theplatinum resistance temperature sensor 40 to measure the temperature ofthe quartz resonator holder 30. The temperature of the measured quartzresonator holder 30 is used as an input value of a thermostat 60connected to the Peltier cooler device 20.

The value input to the thermostat 60 is fedback to control a currentoutput of the thermostat 60 so that temperature of a chill plate in thePeltier cooler device 20 is accurately controlled to be slowly dropped.Slowly dropping the temperature may be performed in the temperaturerange of 0° C. or less to −60° C. or more.

Also, in order to enable the finer temperature control of the quartzresonator holder 30 in the temperature range of 20° C. to −30° C., heatgenerated from a bottom surface of the Peltier cooler device 20 can beeffectively removed. To this end, a heat sink 50 made of copper wherecoolant is circulated may be disposed underneath the Peltier coolerdevice 20.

Preferably, the Peltier cooler device 20 and heat sink 50 isthermal-insulated from a dew-point measurement space so that the changein temperature of the device and the apparatus themselves does not havean effect on the dew-point measurement.

The quartz resonator 10 has a gold electrode surface. The measurement ofthe resonant frequency of the quartz microbalance dew-point sensor isperformed by measuring the resonant frequency of the quartz resonator10. In order words, if the temperature of the quartz resonator 10 isslowly dropped due to the Peltier cooler device 20 and the quartzresonator holder 30, the temperature of the gold electrode surface ofthe quartz resonator 10 is dropped. On the gold electrode surface of thequartz resonator 10 applied with alternating current is derived acondensation phenomenon of water molecule so that the change in theresonant frequency of the quartz resonator 10 is measured. In otherwords, a form that dew begins to form as the temperature of the goldelectrode surface of the quartz resonator 10 is dropped and the resonantfrequency is reduced from beginning of the formation of dew may beappeared.

In order to effectively measure the temperature forming the dew, themeasurement of the resonant frequency is preferably performed at a shorttime interval, for example, the temperature of the quartz resonatorholder 30 and the resonant frequency of the quartz resonator 10 may bemeasured at a time interval of 0.5 second. The measurement of theresonant frequency may be performed by connecting the frequencymeasurement circuit line 70, which is connected to the quartz resonator10, to a frequency counter apparatus located at the outside.

If the temperature is continuously dropped, shock waves are observed atany moment while the reduction of the resonant frequency of the quartzresonator 10 is continued. This means that when the amount of dew formedis increased, the liquid has reached a stage where it cannot becooperated with the vibration of the quartz resonator 10 due to theinertia according to the weight of the liquid. In other words, when thequartz resonator 10 is vibrated in any one direction, the liquid is notsimultaneously moved along with the vibration thereof, i.e., the liquidis not vibrated along with the vibration thereof because of the natureof the liquid intending to move in an existing direction by means of theinertia thereof.

Therefore, the change in the vibration according to the temperature isperturbated so that the graph of the resonant frequency shows anirregularly sudden peak. Consequently, when the peak is observed, it canbe judged that the condensation of water molecule formed on the goldelectrode of the quartz resonator is the liquid dew and the dew pointcan be accurately determined in the frequency region where the resonantfrequency and shock wave of the quartz crystal microbalance.

Since the frost formed is a solid, the sudden reduction of the resonantfrequency is observed. Therefore, whether the dew point is formed or thefrost point is formed cannot be accurately grasped only by means of thesudden reduction pattern of the resonant frequency, however, when theperturbation of such a resonant frequency appears, it can be judged tobe the dew point and when the shock wave is not observed in thereduction region of the resonant frequency after the condensation ofwaterdrops is formed, it means that the solid frost is formed. Thereason is that in this case, the frost sticks to the gold electrodesurface of the quartz resonator so that the inertia effect of the watercondensation does not appear, thereby allowing the shock wave patternnot to appear.

The measurement method of frost point, supercooled dew point, and dewpoint will be described below with reference to FIGS. 2 to 4.

FIG. 2 is a graph showing resonant frequency characteristics accordingto saturated humid air with respect to an ice of −50° C. to surfacetemperature of a quartz resonator in accordance with a first embodimentof the present invention.

Referring to FIG. 2, it can be appreciated that the resonant frequencybegins to suddenly reduce from a temperature of −50° C.±0.2° C. or less.The temperature is ice temperature of a saturation bath in a humiditygenerating apparatus used in the present embodiment. It can beappreciated from this that the temperature is the frost point.

In other words, it means that the state of small waterdrops where theresonant frequency is reduced on the surface of the quartz resonator isthe ice. Also, it is shown that that the vibration is continuously andconstantly reduced by means of further absorption of water molecule inthe air.

The reason is that ice is considered to be rigid so that it can beconsidered to be moved along with the vibration on the surface of thequartz resonator. When the vibration is constantly reduced, it can beappreciated that a deviation between the surface of the quartz resonatorand an interface of an ice layer can be disregarded.

The same tendency is shown when measuring the frost point between −30°C. and −60° C. It can be appreciated from the results that the frostpoint within the temperature can be measured.

FIG. 3 is a graph showing resonant frequency characteristics accordingto a saturated vapor with respect to an ice of −10° C. to the surfacetemperature of the quartz resonator in accordance with a secondembodiment of the present invention, wherein the characteristics of thesaturated vapor with the supercooled dew point and the frost point in aninterval of 0° C. to −30° C. are shown.

Referring to FIG. 3, the vapor used in the present embodiment is humidair saturated using an ice of −10° C. and vapor partial pressure is2.597 mbar. Micro waterdrops on the quartz resonator begin to appear at−11.2° C. It can be appreciated that this is not frost but supercooleddew. The reason is that the saturated vapor pressure in the liquid wateris about 2.605 mbar at −11.2° C. and the saturated vapor pressure in theice is 2.335 mbar at −11.2° C. Also, for the liquid water, the saturatedvapor pressure has relative uncertainty of 0.3% in the temperature rangeof −50° C. to 0° C.

In other words, when comparing a numerical difference of the saturatedvapor pressure and an analysis error of the dew point/frost point on thecurve of the resonant frequency, it can be appreciated that theuncertainty on water of 0° C. or less is associated with the saturatedvapor pressure and is not associated with the accuracy of thesupercooled dew point measured. Therefore, it can be appreciated thatthere is no any error or unreasonable in judging the measuredtemperature to be a liquid state.

It can be appreciated from the curve of the resonant frequency withrespect to the surface temperature of the quartz resonator that theshape of the micro waterdrops formed on the surface of the quartzresonator is divided into different three intervals.

In the case of the interval I, the micro waterdrops formed on thesurface of the quartz resonator can also be ignored due to its smallinertia mass so that the movement of waterdrops is made along with thevibration movement of the surface of the quartz resonator. In otherwords, although the waterdrops are slipped on the surface of the quartzresonator, it is shorter than the vibration period of the quartzresonator. As shown in the interval I, the resonant frequency shows atendency to constantly reduce.

In the case of the interval II, the aggregation of the water molecule iscontinued at the moment that the inertia of the liquid cannot be ignoreddue to an influence of a liquid size aggregated on the surface of thequartz resonator, so that a sliding phenomenon of the liquid occurs. Asa result, the liquid has reached a stage where it cannot be cooperatedwith the vibration of the quartz resonator 10 due to the inertiaaccording to the weight of the liquid.

As described with reference to FIG. 1, the liquid is not simultaneouslymoved along with the vibration of the quartz resonator, that is, theliquid is not vibrated along with the quartz resonator because of thenature of the liquid intending to move in the existing direction bymeans of the inertia thereof so that the sliding phenomenon momentarilyoccurs, thereby showing the phenomenon that the resonant frequency ofthe quartz resonator is bounced. When this peak is observed, it can bejudged to be the dew point.

In the case of the interval III, since a hopping interval of theresonant frequency disappears and at the same time, constantly reducesagain, it can be appreciated that the sliding phenomenon of waterdropsis not shown any more. The dynamical perturbation occurs on thesupercooled dew formed on the surface of the quartz resonator accordingto the rapid vibration movement of the quartz resonator so that phasetransition from the supercooled dew to the frost occurs within rapidtime. That is, it can be appreciated that the dynamical perturbationaccelerates the transition speed.

The transition phenomenon from the supercooled dew to the frost cannotbe measured by means of the existing chilled mirror. For example, in thecase of the interval II, since the temperature reduction speed is 0.1°C./sec, it can be appreciated that the transition speed is below oneminute. Since the speed is the phenomenon that may occur or may notoccur over several hours in the chilled mirror being the optical method,the dew point and frost point cannot be accurately distinguished.

Therefore, the present embodiment can accurately distinguish and measureboth the frost point and the supercooled dew point by scanning onceresonant frequency according to the temperature drop.

FIG. 4 is a graph showing the resonant frequency characteristicsaccording to the surface temperature of the quartz resonator withrespect to the saturated humid air having the saturated vapor pressurewith respect to water of 6.3° C. according to a third embodiment of thepresent invention.

Referring to FIG. 4, as shown in a graph inserted therein, thecondensation temperature of waterdrops is 6.25° C.±0.22° C.

Since this is normal temperature, it can be appreciated that the pointobserved is the dew point. It can be appreciated that the transitionregion shown in FIG. 3 does not appear. Since the surface temperature ofthe quartz resonator is not sufficiently reduced to 0° C. or less, thesupercooled dew is not generated. Consequently, it can be analyzed thatthe transition condition is not formed.

In the case where the dew is generated, it can be appreciated that thesliding phenomenon can be generated by means of the inertia effect ofwaterdrops, likewise the case where the supercooled dew is formed. Asshown in FIG. 4, the reason why the condensation of liquid water isformed on the surface of the quartz resonator and then, the resonantfrequency is rapidly reduced is that the aggregation of water moleculeis caused due to the high vapor partial pressure in the air to rapidlyincrease the mass weighted to the quartz resonator. As in a regioninside a circular indicated by a dotted line, it can be described that afluctuation region of the resonant frequency appears since a phase-lockcondition of the vibration circuit manufactured for measuring theresonant frequency is destroyed due to the sliding phenomenon ofwaterdrops and the overload of mass.

[Industrial Applicability]

While the present invention has been described in connection with alimited embodiments and drawings, they are provided only for helping theunderstandings of the present invention and the present invention is notlimited to the disclosed embodiments. Accordingly, it is to beunderstood that various modifications and changes can be made by thoseskilled in the art from the above description.

Therefore, the scope of the present invention is not limited to thedisclosed embodiments, but is intended to cover various modificationsand equivalent arrangements included within the spirit and scope of theappended claims, and equivalents thereof.

The invention claimed is:
 1. A measurement method of distinguishing dewand frost point using a quartz crystal microbalance dew-point sensor inlow temperature, the method comprises the steps of: measuring a resonantfrequency of a quartz crystal microbalance dew-point sensor whiledropping temperature; observing shock waves of the resonant frequency;and determining dew point or frost point through the observation of theresonant frequency and shock waves of the quartz crystal microbalancedew-point sensor; wherein when observing the resonant frequency of aquartz resonator in the quartz crystal microbalance dew-point sensorwhile dropping temperature, it is judged that the temperature is the dewpoint if a transition phenomenon of the shock wave and the resonantfrequency is observed in a resonant frequency pattern of the quartzresonator and the temperature is the frost point if the transitionphenomenon of the shock wave and the resonant frequency is not observed.2. The method according to claim 1, wherein before the shock wave of theresonant frequency is observed, the resonant frequency is constantlyreduced.
 3. The method according to claim 2, wherein after the shockwave of the resonant frequency is observed, the resonant frequency isconstantly reduced again.
 4. The method according to claim 1, whereindropping the temperature is performed in the range of 0° C. or less to−90° C. or more.
 5. The method according to claim 1, wherein the quartzcrystal microbalance dew-point sensor comprises a quartz resonator, aPeltier cooler device, a quartz resonator holder, and a platinumresistance temperature sensor.
 6. The method according to claim 5,wherein dropping the temperature is performed by controlling thetemperature of the quartz resonator using the Peltier cooler device. 7.The method according to claim 6, wherein the temperature dropped bymeans of the Peltier cooler device is transferred to the quartzresonator through the quartz resonator holder so that the temperature ofthe quartz resonator is controlled.
 8. The method according to claim 7,wherein the quartz resonator holder is made of copper and one surface ofthe quartz resonator holder is attached with the platinum resistancetemperature sensor to measure the temperature of the quartz resonatorholder.